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Abstract:

The object of the present invention is to prevent damages of a vibration
isolating rubber and cracks in a welded portion of a sub-frame when
press-fitting a sub-frame mount.
The sub-frame mount 1 comprises an outer cylinder 2, an inner cylinder 2
and the vibration isolating rubber 4 connecting these outer and inner
cylinders. A small diameter portion 10 and a large diameter portion 11
are provided on a lateral wall of a barrel portion of the outer cylinder
2. Between the small diameter portion 10 and the large diameter portion
11 is formed a step-like boundary portion 12. The height in the axial
direction of the boundary portion 12 changes in the circumferential
direction and has a substantially mountain-like shape with a top 12a
projecting in the press fitting direction. A contact area of the large
diameter portion 11 contacting a mounting hole 21 of the sub-frame 20 is
increased in accordance with an amount of the press fitting. Therefore,
when the sub-frame mount 1 is press-fitted into the mounting hole 21 of
the sub-frame 20, the press fitting load is gradually increased thereby
preventing the rapid rise of the press fitting load.

Claims:

1. A cylindrical vibration isolating device comprising an inner cylinder
and an outer cylinder being connected through a vibration isolating
rubber, a small diameter portion and a large diameter portion being
provided on a lateral wall of a barrel portion of said outer cylinder,
wherein a boundary portion between said small diameter portion and said
large diameter portion is changed in height in an axial direction of said
outer cylinder such that, when said outer cylinder is press-fitted into a
mounting hole provided in a mounted member, a contact area between an
inner peripheral wall of said mounting hole and said large diameter
portion is gradually increased.

2. The cylindrical vibration isolating device according to claim 1,
wherein said boundary portion is formed substantially in a shape of a
mountain and a top of said boundary portion projects on a forward side at
a time of press fitting.

3. The cylindrical vibration isolating device according to claim 2,
wherein said top and a bottom of said boundary portion are arranged
alternately and in pairs respectively in a circumferential direction of a
lateral wall of said outer cylinder, a pair of tops and a pair of bottoms
are opposite to each other across a center axis of the device
respectively, and said tops of said boundary portion are located in one
of two orthogonal directions meeting at right angles with an axis of said
outer cylinder while said bottoms are located in the other of said two
orthogonal directions.

4. The cylindrical vibration isolating device according to claim 3,
wherein an axially extending cavity is formed in said vibration isolating
rubber in a vicinity of said top of said boundary portion, and a solid
connecting leg for connecting said inner cylinder and said outer cylinder
is formed in said vibration isolating rubber in Ha vicinity of said
bottom.

5. The cylindrical vibration isolating device according to claim 4,
wherein multiple stoppers each of which axially projects from an end in
an axial direction of said vibration isolating rubber are provided in the
circumferential direction, said stoppers are provided in positions
corresponding to said cavity and said connecting leg, and said stopper
corresponding to said cavity projects greater than said stopper
corresponding to said connecting leg.

6. The cylindrical vibration isolating device according to claim 1,
wherein a forward end portion at a time of mounting is formed as an
engaging head portion of said vibration isolating rubber which projects
from said outer cylinder.

[0004]As an example of cylindrical vibration isolating devices in which an
inner cylinder and an outer cylinder are connected by a vibration
isolating rubber, there is known a sub-frame mount. This sub-frame mount
is the cylindrical vibration isolating device having the inner and outer
cylinders connected by the vibration isolating rubber, and has a large
diameter portion formed of a vibration isolating rubber or the like on a
partial surface of the outer cylinder. The large diameter portion is
adapted to be press-fitted into a mounting hole of the sub-frame (as an
example, see a patent reference 1).

[0006]FIG. 11 is a graph showing a change in a press fitting load when the
sub-frame mount is press-fitted into the mounting hole provided in the
sub-frame, wherein the vertical axis denotes the press fitting load and
the horizontal axis denotes a press fitting stroke (a press fitting
amount). A conventional sub-frame mount "a" shown in this graph is
comprised of a flange "b" on one end thereof in the axial direction, a
rubber seal "c" on the other end thereof, a large diameter portion "d"
and a small diameter portion "e" on a middle barrel portion.

[0007]When this sub-frame mount "a" is press-fitted from the rubber seal
portion "c" into the mounting hole of the sub-frame, firstly a
comparatively small change of the press fitting load due to the change of
the rubber seal portion "c" is created between a point P1 and a point P0.
Next, when the large diameter portion "d" comes into contact with the
mounting hole at the point P0, the press fitting load goes up rapidly to
be a straight line of an acute angle between the point P0 and a point P4.
This rapid rise of the press fitting load causes such a bad influence
that the rubber seal portion "c" is damaged or that a crack is developed
in a welded portion of the sub-frame.

[0008]Therefore, an object of the present invention is to prevent the
rapid rise of the press fitting load.

SUMMARY OF THE INVENTION

[0009]To solve the above mentioned problem, in a first aspect of the
present invention, a cylindrical vibration isolating device comprises an
inner cylinder and an outer cylinder being connected through a vibration
isolating rubber, a small diameter portion and a large diameter portion
being provided on a lateral wall of a barrel portion of the outer
cylinder, wherein a boundary portion between the small diameter portion
and the large diameter portion is changed in height in an axial direction
of the outer cylinder such that, when the outer cylinder is press-fitted
into a mounting hole provided in a mounted member, a contact area between
an inner peripheral surface of the mounting hole and the large diameter
portion is gradually increased.

[0010]In a second aspect of the present invention, the boundary portion is
formed substantially in the shape of a mountain and a top of the boundary
portion projects on a forward side at the time of press fitting.

[0011]In a third aspect of the present invention, the top and a bottom of
the boundary portion are arranged alternately and in pairs respectively
in the circumferential direction on the lateral wall of the outer
cylinder, wherein the pair of tops and the pair of bottoms are opposite
to each other across a center axis of the device respectively, and the
tops of the boundary portion are located in one of two orthogonal
directions meeting at right angles with an axis of the outer cylinder
while the bottoms are located in the other of the two orthogonal
directions.

[0012]In a fourth aspect of the present invention, an axially extending
cavity is formed in the vibration isolating rubber in the vicinity of the
top of the boundary portion, and a solid connecting leg for connecting
the inner cylinder and the outer cylinder is formed in the vibration
isolating rubber in the vicinity of the bottom.

[0013]In a fifth aspect of the present invention, multiple stoppers each
of which axially projects from an end in the axial direction of the
vibration isolating rubber are provided in the circumferential direction,
wherein the stoppers are provided in positions corresponding to the
cavity and the connecting leg, and the stopper corresponding to the
cavity projects at a higher level than the stopper corresponding to the
connecting leg.

[0014]In a sixth aspect of the present invention, a forward end portion at
the time of mounting is formed as an engaging head portion of vibration
isolating rubber which projects from the outer cylinder.

[0015]According to the invention as defined in the first aspect, since the
boundary portion is changed in height in the axial direction of the outer
cylinder such that the contact area between the inner peripheral surface
of the mounting hole and the large diameter portion is gradually
increased, when the outer cylinder is press-fitted into the mounting hole
provided in the mounted member, the press fitting load at the time of
press fitting is gradually increased in accordance with the press fitting
stroke so that there is no rapid rise in the press fitting load thereby
to prevent the bad influence by the rapid rise in the press fitting load.

[0016]According to the invention as defined in the second aspect, since
the boundary portion is formed substantially in an inverted U-shape, the
rapid rise preventing structure of the press fitting load can be easily
formed.

[0017]According to the invention as defined in the third aspect, the tops
and bottoms of the boundary portion are oppositely arranged alternately
and in pairs respectively, and the tops are located for example in an X
direction of two orthogonal directions (hereinafter, referred to as X
direction and Y direction) meeting at right angles with an axial
direction (hereinafter, referred to as Z direction) of the outer cylinder
while the bottoms are located in the Y direction. Therefore, the press
fitting load has a directional property. It is possible to make the press
fitting load greater only in the necessary direction (for example, in the
X direction).

[0018]According to the invention as defined in the fourth aspect, the
axially extending cavity is formed in the vibration isolating rubber in
the vicinity of the top of the boundary portion, and the solid connecting
leg for connecting the inner cylinder and the outer cylinder is formed in
the vibration isolating rubber in the vicinity of the bottom, so that it
is possible to decrease the influence upon spring of the vibration
isolating rubber because of reduction of the diameter of the outer
cylinder at the time of press fitting.

[0019]According to the invention as defined in the fifth aspect, the
vibration isolation rubber is weak in the spring of the X direction and
strong in the spring of the Y direction for example, by provision of the
cavity and the connecting leg. Therefore, when torsion is generated in
relation to the inner cylinder, the side of the cavity (in this case, the
X direction) becomes weak in relation to the torsion. However, since
multiple stoppers each of which axially projects from an end in the axial
direction of the vibration isolating rubber are provided in the
circumferential direction, corresponding to the cavity and the connecting
leg, and the stopper corresponding to the cavity projects at a higher
level than the stopper corresponding to the connecting leg, the weak
spring side can be stiffened strongly by the higher stopper, and the
spring against the torsion can be controlled such that it becomes the
same level as the connecting leg side.

[0020]According to the invention as defined in the sixth aspect, since the
forward end portion at the time of mounting is formed as the engaging
head portion of vibration isolating rubber which projects from the outer
cylinder, the vibration isolating rubber of the engaging head portion can
be kept free without restraint of the outer cylinder until mounting.
Therefore, the vibration isolating rubber can be released from a molding
deformation before mounting, thereby making it possible to improve the
durability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a perspective view of a sub-frame mount according to the
first embodiment of the present invention;

[0022]FIG. 2 is a perspective view of the sub-frame mount which is turned
upside down from FIG. 1;

[0023]FIG. 3 is a bottom view of the sub-frame mount;

[0024]FIG. 4 is a front view of the sub-frame mount;

[0025]FIG. 5 is a side view of the sub-frame mount;

[0026]FIG. 6 is a cross sectional view taken on the line 6-6 of FIG. 3;

[0027]FIG. 7 is a cross sectional view taken on the line 7-7 of FIG. 3;

[0028]FIG. 8 is a cross sectional view taken on the line 8-8 of FIG. 5;

[0029]FIG. 9 is a cross sectional view taken on the line 9-9 of FIG. 5;

[0030]FIG. 10 is a partial cross sectional view taken along the line 6-O-7
of FIG. 3;

[0031]FIG. 11 is a graph showing the change in press fitting load; and

[0032]FIG. 12 is a front view showing another embodiment of the sub frame
mount.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033]Hereinafter, an embodied example applied to a sub-frame mount will
be explained with reference to the accompanying drawings, wherein FIG. 1
is a perspective view of the sub-frame mount according to the first
embodied example of the present invention, FIG. 2 is a perspective view
thereof which is turned upside down, FIG. 3 is a bottom view thereof,
FIG. 4 is a front view thereof, FIG. 5 is a side view thereof, FIG. 6 is
a cross sectional view taken on the line 6-6 of FIG. 3, FIG. 7 is a cross
sectional view taken on the line 7-7 of FIG. 3, FIG. 8 is a cross
sectional view taken on the line 8-8 of FIG. 5, FIG. 9 is a cross
sectional view taken on the line 9-9 of FIG. 5, and FIG. 10 is a partial
cross sectional view taken along the line 6-O-7 of FIG. 3. In this
embodied example, each direction of the sub-frame mount such as an upper
and lower direction, a forward and backward direction and a right and
left direction is fixed on the basis of a mounted state on the vehicle
body, Moreover, orthogonal three-axis directions of X, Y and Z correspond
to the forward and backward direction, the right and left direction and
the upper and lower direction respectively.

[0034]Referring now to these drawings, the sub-frame mount 1 comprises an
outer cylinder 2 and an inner cylinder 3 each made of metal, and a
vibration isolating rubber 4 for connection between the outer cylinder 2
and the inner cylinder 3. The vibration isolating rubber 4 is an
elastomer constituting the core of vibration isolation and is made of a
rubber of proper composition. The vibration isolating rubber is formed by
a known method that it is vulcanized and adhered integrally to the outer
cylinder 2 and the inner cylinder 3 or that it is molded separately and
then adhered integrally to them. In FIG. 1 and FIG. 2 there is seen an
engaging head portion 5 of the vibration isolating rubber 4. The
reference character 6 denotes a bored hole in the shape of an axially
extending cavity, and the reference character 7 in FIG. 2 is a recess
formed by connection between open ends of the opposed bored holes 6.

[0035]The outer cylinder 2 comprises a small diameter portion 10 and a
large diameter portion 11 formed on a lateral wall of a cylindrical
barrel portion, a boundary portion 12 formed in the shape of a step on
the boundary between these small and large diameter portions, and an
outer flange 13 formed at an end (lower end) in the axial direction of
the barrel portion. The reference character 14 denotes a positioning
means of a notch shape formed on the outer flange 13 for locating the
position at the time of mounting on the sub-frame as described later.

[0036]As shown in FIG. 2 and FIG. 3, in a lower end portion (an upper end
in the illustrated state) of the vibration isolating rubber 4 there is
integrally formed a cover portion 9 for covering the outer flange 13.
Stoppers 8A and 8B are formed integrally on this cover portion 9 in a
state of projecting therefrom. The four stoppers 8A and 8B are provided
at intervals of 90° and each formed on an X axis or a Y axis.
Herein, the stoppers in the X direction are denoted by 8A while the
stoppers in the Y direction are denoted by 8B.

[0037]As shown in FIG. 4, the boundary portion 12 is formed substantially
in an inverted U-shape or in the shape of a mountain such as to project
upwardly toward a central top portion 12a. As shown in FIG. 5, the small
diameter portion 10 extends downwardly approximately to a half or more of
axial length of the outer cylinder 2 in the Z direction. A bottom portion
12b of the boundary portion 12 is formed in the shape of a straight line.
An intermediate portion of the boundary portion 12 extends from the
bottom portion 12b to the top portion 12a while drawing a curve. The
distance between ridgelines on both sides in the circumferential
direction of the top portion 12a is tapered upwardly (see FIG. 4). In
FIG. 4, the reference character 20 denotes a sub-frame on which the
sub-frame mount 1 is mounted, and the reference character 21 denotes a
mounting hole.

[0038]As shown in FIG. 6, the bored hole 6 is provided in pairs in front
and in the rear across a center axis and is formed with a downwardly open
blind hole which extends from the bottom of the vibration isolating
rubber 4 to the position in the vicinity of the upper end thereof. The
provision of the bored hole 6 makes the spring rate in the X direction
lower. An axial end of the bored hole 6 is expanded and connected to the
recess 7. The distance "a" between a seal portion 5a and the top portion
12a is small so that the large diameter portion 11 comes into contact
with an inner wall of the mounting hole 21 (see FIG. 4) from the
beginning of the press fitting of the sub-frame 1.

[0039]An upper end 15 of the outer cylinder 2 is planted in and united
with the inside of the engaging head portion 5. On the outer periphery of
the engaging head portion 5 there is provided the outwardly protruded
seal portion 5a which tightly contacts and waterproofs an inner wall of
the mounting hole 21 when press-fitting the sub-frame mount 1 from a
lower side into the mounting hole 21 of the sub-frame 2 as shown in FIG.
4 on which the sub-frame mount is mounted. The outer diameter of the seal
portion 5a is formed larger than the inner diameter of the mounting hole
21.

[0040]As shown in FIG. 7, there is formed no bored hole 6 in the right and
left direction of the vibration isolating rubber 4 but there is formed a
solid connecting leg 16 for connecting the outer cylinder 2 and the inner
cylinder 3. The spring rate in the Y direction of the vibration isolating
rubber 4 becomes higher by this connecting leg 16. Namely, there is a
difference in the magnitude of the spring rate in the X direction and
that in the Y direction so that the spring ratio between the X direction
and the Y direction is varied. This spring ratio may be freely controlled
by varying the size or the like of the bored hole 6 and the connecting
leg 16. The distance "b" between the seal portion 5a and the bottom
portion 12b is greater (a<b) in the right and left direction, so that
in the right and left direction the large diameter portion 11 is
prevented for a while after starting the press fitting of the sub-frame
mount 1 from coming into contact with the inner wall of the mounting hole
21.

[0041]On an outer periphery of an upper end of the inner cylinder 3 there
is provided an enlarged portion 17 which protrudes outwardly in a radial
direction in such a way as to run up onto an inner periphery of an upper
end of the vibration isolating rubber 4 and to be united therewith. In
this embodied example, the vibration isolating rubber is formed by being
vulcanized after filling a space between the outer cylinder 2 and the
inner cylinder 3 with the vibration isolating rubber 4. At the time of
this vulcanization, the vibration isolating rubber 4 adheres to the outer
cylinder 2 and the inner cylinder 3 so as to be united therewith. As
described above, however, another method of forming the vibration
isolating rubber 4 may be applied.

[0042]A groove 5b is formed on an upper end wall of the engaging head
portion 5 in the vicinity of the enlarged portion 17. This groove 5b has
different widths in a cross section in the X direction and in a cross
section in the Y direction, and the cross section in the X direction is
narrower. The cross section in the Y direction has a cutout portion 5c on
an upper outward side of the groove 5b so as to be open outwardly. An
upper stopper 5d is provided to project upwardly on an outer peripheral
side of the groove 5b. A portion of this upper stopper 5d is lowered to
form the cutout portion 5c.

[0043]The inner cylinder 3 has a cylindrical bottom 18 in which a through
hole 19 is formed. Into this through hole 19 is inserted a bolt 23 which
projects upwardly from a vehicle body frame 22. The bolt 23 passes
through the inside of the inner cylinder upwardly and is fixedly fastened
by a nut 25 through the intermediary of a plate 24 which contacts the
upper side of the upper stopper 5d. The upper stopper 5d is formed
integral with the engaging head portion 5, so that a separate upper
stopper which conventionally is mounted on the upper end of the inner
cylinder 3 can be omitted. Further, the lower ends of the stoppers 8A and
8B projecting downwardly from the lower end of the vibration isolating
rubber 4 also contact or come close to the vehicle body frame 22.

[0044]A clearance "d" is provided between the small diameter portion 10
and the inner wall of the mounting hole 21, and because of this clearance
"d", the small diameter portion 10 does not come into contact with the
inner wall of the mounting hole 21 so as not to generate the press
fitting load. The large diameter portion 11 comes into tight contact with
the inner wall of the mounting hole 21 so that the press fitting load is
generated in accordance with the dimensions of contact area. The outer
flange 13 contacts with the lower end surface of the sub-frame mount 20
and locates the position of the sub-frame mount 21 in the upper and lower
direction.

[0045]The bored hole 6 does not pass through the full length of the
vibration isolating rubber 4 but is open downwardly while an upper end 6a
thereof ends at the level of the engaging head portion 5. The engaging
head portion 5, which is formed by the solid portion of the vibration
isolating rubber 4 and connected to the connecting leg 16, comes into
direct contact with the inner wall of the mounting hole 21 without having
the outer cylinder 2 provided around the outer periphery thereof. On the
outer periphery of the engaging head portion 5 there are formed an
annular seal portion 5a of corrugated cross section in plural stripes
which is elastically deformed to come into tight contact with the inner
wall of the mounting hole 21 when the engaging head portion 5 is
press-fitted into the mounting hole 21. The seal portion 5a has a larger
outer diameter (before mounting) than the outer diameter of the large
diameter portion 11.

[0046]The engaging head portion 5 is press-fitted into the mounting hole
21 without interposition of the outer cylinder 2, and the outer
peripheral portion thereof constitutes an elastomer contact portion
against the inner peripheral portion of the mounting hole 21. The
engaging head portion 5 at the time of press fitting is compressed and
elastically deformed while repeating compression and tension by
displacement in the forward and backward direction and in the right and
left direction of the sub-frame mount 1. The large diameter portion 11
constitutes a metal contact portion. The small diameter portion 10
constitutes a non-contact portion against the mounting hole 21.

[0047]Further, the engaging head portion 5 is kept free without restraint
of the periphery thereof by the outer cylinder 2 until it is press-fitted
into the mounting hole 21. Therefore, the molding deformation
(vulcanizing deformation) of the vibration isolating rubber 4 created
when the vibration isolating rubber 4 is formed integral with the outer
cylinder 2 and the inner cylinder 3 is released for the most part before
being press-fitted into the mounting hole 21 whereby it is possible to
decrease the molding deformation. Thus, the durability can be improved.

[0048]As shown in FIG. 8, the small diameter portion 10 is formed by being
narrowed in the right and left direction. The end of the bored hole 6 is
located in the vicinity of the inside of the boundary portion 12. The
bored hole 6 is provided inside of the large diameter portion 11, and the
opening portion thereof is formed in the shape of a circular arc of the
larger radius of curvature than that of the large diameter portion 11 and
extends to the position close to the small diameter portion 10 on both
sides of an X axis. This bored hole is provided in pairs in front and
behind across the inner cylinder 3.

[0049]As shown in FIG. 9, in the lower portion of the outer cylinder 2 the
small diameter portion is not formed but only the large diameter portion
11 is provided. Therefore, the large diameter portion 11 has a single
ring shape of a prefixed diameter in circumference.

[0050]As shown in FIG. 10, the stoppers 8A and 8B are provided in pairs to
be four pieces in total, the respective pair being opposed to each other
while crossing the X axis or the Y axis. The stoppers 8A and 8B are
different in height. Namely, the stopper 8A in the X direction is higher
by H than the stopper 8B in the Y direction so as to project by H
downwardly.

[0051]With this structure, the control of the spring ratio against torsion
becomes possible. That is, the spring rate in the X direction and in the
Y direction of the vibration isolating rubber 4 itself is small in the X
direction due to the bored hole 6 and large in the Y direction due to the
connecting leg 16. Accordingly, if the stoppers are identical in the X
direction and in the Y direction, the spring rate against torsion in the
X direction ought to be smaller than the spring rate in the Y direction
when the torsion with respect to the Z axis acts on the inner cylinder 3.

[0052]However, as the stopper 8A in the X direction is higher by the
projecting height H than the stopper 8B in the Y direction, by this
stopper 8A an interference at the time of the torsional deformation
becomes greater than that of the stopper 8B in the Y direction so as to
make the spring rate larger for that, so that the spring rate against
torsion in the X direction can be adjusted at the same level as that in
the Y direction, thereby making it possible to equalize the spring rate
against torsion.

[0053]This means that the control of the spring ratio against torsion in
the X direction and in the Y direction can be done freely. By adjusting
the projecting height H of the stopper 8A in relation to the stopper 8B,
the spring ratio in the X direction and in the Y direction is able to be
freely controlled. Moreover, the spring rate in the Y direction is able
to be freely increased. In this case, the projecting height of the
stopper 8B is increased or the sub-frame mount 1 is tuned 90° and
mounted.

[0054]Next, the operation of this embodied example will be explained
hereunder. As shown in FIG. 4, the sub-frame mount 1 is press-fitted into
the mounting hole 21 of the sub-frame 20 while inserting the engaging
head portion 5 first from the bottom of the mounting hole 21. Then, the
engaging head portion 5 including the seal portion 5a is inserted into
the mounting hole 21 as it is compressed and deformed. At this time,
since because of existence of the small diameter portion 10, the outer
cylinder 2 does not contact the inner wall of the mounting hole 21, the
engaging head portion 5 is able to be press-fitted into the mounting hole
21 under light press fitting load. Thereafter, when the large diameter
portion is press-fitted, it comes into contact with the inner wall of the
mounting hole 21 so as to have the press fitting load increased. Then,
since there is the difference in the contact area between the X direction
and the Y direction, and since the distance between the seal portion 5a
and the top portion 12a is small in the forward and backward (X)
direction, the load becomes greater from the beginning of the press
fitting. However, since the distance "a" between the seal portion 5a and
the bottom portion 12b is large, the load is not increased until
approaching the end of the press fitting.

[0055]Moreover, the boundary portion 12 is formed in the shape of slope
gradually expanding its diameter from the small diameter portion 10 to
the large diameter portion 11 and also formed in the shape of a curved
line in the direction facing from the top portion 12a to the bottom
portion 12b in such a manner that the distance between both sides of the
top portion 12a is tapered upwardly. Accordingly, the press fitting load
is gradually increased. Thus, since the press fitting load is able to be
gradually increased without rapid increase, the press fitting operation
may be performed easily and it is possible to prevent the damage of the
vibration isolating rubber 4 and the generation of cracks in the welded
portion on the side of the sub-frame 20.

[0056]The change of this press fitting load will be explained with
reference to FIG. 11. Firstly when the engaging head portion 5 is
press-fitted at a starting point P1 of the press fitting, the press
fitting load rises at comparatively small value and in the less change
state of a gentle slope. When the top portion 12a comes into contact with
the inner wall of the mounting hole at the point P2, the load is
increased slightly. Thereafter, the press fitting load is gradually
increased with gradual increase of the contact area until the bottom
portion 12b contacts the inner wall of the mounting hole at the point P3.
At this time, the slope of line P2-P3 is more than the slope of line
P1-P2 and less than the slope of line P3-P4. When reaching the point P3,
an entire periphery of the large diameter portion 11 contacts the inner
wall of the mounting hole, so that the load is increased rapidly in the
same manner as the conventional example. When reaching the point P4, the
outer cylinder comes into contact with the inner wall of the mounting
hole. The line P3-P4 corresponds to a straight line P0-P4 of the
conventional example.

[0057]As described above, in comparison with the points P2-P0-P3 of the
conventional example as shown in dashed line, since in this embodied
example it is possible to change the press fitting load like the line
P2-P3 of a little steeper slope than the line P2-P0, the press fitting
load is able to be changed in three stages of gradually increased slopes
like the line P1-P2, the line P2-P3 and the line P3-P4 without the rapid
change of the press fitting load as developed at the point P0 in the
conventional example. Therefore, the rapid rise of the press fitting load
can be prevented and the bad influence upon the vibration isolating
rubber 4 and the sub-frame 20 can be avoided.

[0058]Moreover, it is possible to freely adjust the slope or the like of
the line P2-P3 by adjusting an angle of the slope changing from the small
diameter portion 10 to the large diameter portion 11 of the boundary
portion 12, and the variation from the top portion 12a to the bottom
portion 12b (an angle of the ridgeline as shown in FIG. 4). Also, if the
variation from the top portion 12a to the bottom portion 12b is changed
in multiple stages, it is possible to change the press fitting load more
between the points P2-P3 in the multiple stages.

[0059]Furthermore, when the contact area of the large diameter portion 11
is larger and the contact area of the small diameter portion 10 is
smaller in the forward and backward direction, the forward and backward
direction (X direction) which is a reference of fixation with respect to
the sub-frame 20 in the X plane and Y plane can be firmly fixed on the
sub-frame 20. However, when the right and left direction (Y direction) is
used as the reference, the contact area of the large diameter portion 11
may be made largest in the Y direction by having turned 90°.

[0060]Further, since the top portion 12a is provided in the vicinity of
the seal portion 5a, and since the distance between the seal portion 5a
and the top portion 12a is small, the top portion 12a is able to be in
contact with the inner wall of the mounting hole 21 from the beginning of
the press fitting, so that the forward and backward direction can be used
as a guide at the time of the press fitting.

[0061]FIG. 12 is a front view of another embodied example of which the
shape of the boundary portion 12 is modified. In this example, the
boundary portion 12 is formed in the shape of a triangular mountain or a
chevron with a top portion of an acute angle. As formed like this, the
contact area at the time of the press fitting is able to be lessened
thereby having the press fitting load decreased so that the press fitting
operation can be easily performed. Like this, the shape of the boundary
portion 12 can be varied from the one of a straight line to the one of a
curved line. In addition, the curved line shape also can be varied freely
in accordance with the press fitting load to be selected.

[0062]It is to be understood that the present invention is not limited to
each of the above described embodied examples, and that modifications and
applications may be variously made within the scope and sprit of the
invention. For example, the present invention is applicable to various
kinds of known cylindrical vibration isolating devices such as a
suspension bushing, etc. other than the sub-frame mount.